1. Field of the Invention
The present invention relates to a carrier touch sensing system, and more particularly, to a carrier touch sensing system capable of performing phase calibration and carrier signal demodulation via in-phase and quadrature demodulations.
2. Description of the Prior Art
A touch display device provides intuitional and easy operations and has been widely utilized among electrical products. In general, a touch display device may be composed of a display panel and a touch panel, wherein the touch panel may include a plurality of driving electrodes, a plurality of receiving electrodes and a demodulation circuit. Traditionally, the driving electrodes of the touch panel are sequentially and respectively inputted with an impulse signal, the receiving electrodes of the touch panel receive sensing signals induced by the impulse signal. The demodulation circuit detects a touch event on the touch panel and a location corresponding to the touch event according to the sensing signals, so as to generate a touch signal and realize a function of touch control.
Recently, a carrier touch sensing system is introduced to the industry to improve the function of touch control. A touch panel for the carrier touch sensing system is inputted with carrier signals instead of an impulse signal, wherein the carrier signals may be sinusoidal waves such as sine-waves or cosine-waves.
During propagation of the carrier signals in the touch panel, carrier sensing signals received by a demodulation circuit may have phase delays due to different characteristics of the touch panel, such as production procedures, operating performances, environment temperatures, noise interferences, and so on. Without considering the phase delays of the carrier signals, the demodulation circuit may generate wrong touch signals. In such a situation, once the carrier touch sensing system is integrated with other electronic devices, such as a display, a smart phone, a tablet computer, or a laptop computer, the wrong touch signals may cause problems regarding touch controls.
In addition, the phase delay varies due to operating conditions of the touch panel; in other words, the phase delays need to be calibrated under certain operating conditions to maintain a signal integrity of the touch signals.
Therefore, how to demodulate the carrier sensing signals to generate the correct touch signals and the phase delay and calibrate the phase delays has become a critical issue in the industry.